The present invention relates to hydrocarbon oil catalytic cracking catalyst compositions and, in more specifically, relates to catalyst compositions which display a high cracking activity when used in the catalytic cracking of hydrocarbon oils, but produce lower amounts of coke and impart superior thermally stability despite said high cracking activity.
As the original object of hydrocarbon catalytic cracking consists in the production of gasoline, it is natural that the catalyst used should be high in catalytic activity and gasoline selectivity. But, there has usually been a common evil in that a catalyst being high in catalytic activity produces a large quantity of coke.
In recent years, however, crude oil supply circumstances have changed to bring about the situation where low grade heavy hydrocarbon fractions containing heavy metals such as vanadium, nickel, iron, copper and the like, typically residual oils, must be used as catalytic cracking materials. In the case of catalytic cracking low grade heavy hydrocarbons, however, as the degree of metallic contaminants contained in feed stock being deposited on the catalyst is heightened, the cracking activity of the catalyst is destroyed by this extraordinary deposition of metals.
In addition, said catalytic cracking is disadvantageous in that the metals deposited on the catalyst accelerate the dehydrogenating reaction and thus promote the production of hydrogen and coke.
As catalytic compositions which display a high cracking activity when used in the catalytic cracking of hydrocarbons but produce low amounts of hydrogen and coke, there is, for instance, Japanese Laid-open patent application No. 177138/1984 which discloses catalytic compounds which comprise combinations of silica and stabilized Y zeolite. Japanese Published patent application No. 5748/1972 teaches catalytic compositions which comprise dispersed crystalline zeolite particles in phosphate solution-treated silica-magnesia.
Japanese Laid-open patent application No. 214344/1983 further discloses that a catalytic composition, containing the hydrogen type faujasite Y prepared by the use of clay as starting material and the residue derived from said clay (silica-alumina), is improved in catalytic activity when treated by a phosphorus compound.
The usual catalytic, cracking catalysts including the above-mentioned catalyst compositions, when contacted with hydrocarbon materials under conversion reaction conditions, unavoidably produce by-product coke. Said coke deposits on the catalyst surface. The heavier the hydrocarbon, the more the deposition of coke is increased.
Generally speaking, it is common in the catalytic cracking process that the catalyst, whose activity has been deteriorated by the deposition of coke, is regenerated to restore its activity, and thereafter recycled to the conversion region. The object of said catalyst regeneration step is to subject the coke deposited on the catalyst surface to combustion-removal. Accordingly, it is preferable that the catalytic cracking catalysts should be thermally stable to such an extent that their catalytic performance may not be thermally destroyed even when exposed repeatedly to high temperatures under the steam atmosphere of the regeneration step. However, the fact is that the usual catalytic cracking catalysts are not always possessed of sufficient thermally stability.